Andras Kis

Modern short-scale information transmission mainly relies on dissipative charge transport, with electrons scattered by defects and phonons, leading to significant power losses. By contrast, excitons—charge-neutral quasiparticles—offer a playground for electro-optical energy-efficient information transduction and processing owing to their extended lifetimes, charge neutrality and efficient electrostatic control. In this work, we report the observation of fast exciton transport in a van der Waals heterostructure over distances exceeding 10 µm, constrained only by the heterostructure finite size. We observe the presence of excitonic potential ramps that leads to long-range rapid exciton drift and enables rapid dilution of the initial exciton population. Our measurements reveal fast exciton propagation, with interlayer exciton drift velocities of approximately 2.66 × 10 ⁴ m s ⁻¹ , within a transport regime that remains robust across a wide range of exciton densities and temperatures up to 150 K. Our work opens avenues for the development of high-speed, energy-efficient excitonic devices, such as field-effect switches and modulators.

The past decade has seen rapid growth in the number of experimentally realized two-dimensional (2D) materials with diverse chemical and physical properties. However, information on their crystal structure, synthesis routes, and measured or predicted properties remains scattered across thousands of publications. Here, we consolidate this fragmented knowledge by establishing X2DB─an open infrastructure that integrates experimental and computational data on 2D materials. Using extensive literature mining and direct community uploads, we identify 370 unique 2D materials that have been realized in monolayer or few-layer form and link them to their digital counterparts in computational databases, enabling consistent ab initio characterization of their properties across monolayer, bilayer, and bulk forms. We describe the structure and content of the database, highlight its support for community uploads, illustrate how it can be used to generate scientific insight, and introduce a hierarchical classification of the known set of 2D materials. Our work supports the integration and cross-fertilization of experimental and theoretical knowledge and contributes to data-driven and predictive synthesis of 2D materials.

Strain is a proven technique for modifying the bandgap and enhancing carrier mobility in 2D materials. Most current strain engineering techniques rely on the post‐growth transfer of these atomically thin materials from growth substrates to target surfaces, limiting their integration into nanoelectronics. Here, we present a new approach where strain in 2D materials is already introduced directly during their growth on grayscale‐patterned topographies instead of flat surfaces. Both strain levels and orientations are deterministically engineered by controlling grayscale surface contour lengths through thermal expansion mismatches in nanostructured stacks, where the conformally grown and firmly attached 2D material is forced to match the underlying morphology change during cooling. With this method, we experimentally demonstrate precise control of localized tensile strain from 0 to 0.5% in grown MoS ₂ monolayer along both uni‐ and multiaxial directions, while higher strain levels are shown to be theoretically possible. This strain‐engineered growth of 2D material films directly on the target substrates is a generic and adaptable approach to various combinations of grayscale‐thin‐film/substrates and eliminates all the transfer‐related limitations of previous approaches, thus paving the way for integrating strained 2D materials into next‐generation nanoelectronics.

Metallic two-dimensional (2D) transition metal dichalcogenides (TMDCs) are garnering significant attention for their ability to enhance device performance when used as 2D contacts with semiconducting 2D materials, as well as for their intriguing low-temperature properties, including superconductivity, magnetism, and charge density waves (CDWs). However, the advancement of both fundamental studies and practical applications has been hindered by challenges in synthesizing high-quality, large-area materials. In this work, we report the epitaxial growth of wafer-scale 2D superconducting TMDC single-crystal multilayers by metal–organic chemical vapor deposition (MOCVD). Our NbS₂ multilayer films achieve high wafer-scale uniformity and single crystallinity of 2H phase, as confirmed by AFM, Raman spectroscopy, SHG mapping, LEED and STEM measurements. This is enabled by a dual-precursor strategy that drives self-templated concurrent epitaxy on lattice-matched sapphire, which is further supported by a kinetic growth model. Devices fabricated from the NbS₂ film demonstrate superconductivity below a transition temperature of 3 K, consistent with a Berezinskii-Kosterlitz-Thouless (BKT) type superconducting phase transition, with an impressive yield of 95.1% and a resistance variation of only 12%. Additionally, we demonstrate the wafer-scale growth of superconducting NbSe₂ films (T_c = 5 K) via MOCVD. Our work underscores a versatile and scalable approach for synthesizing wafer-scale 2D superconductor single crystals, which is essential for their integration into next-generation TMDC-based electronic devices.

Extended efforts have been devoted to the study of strongly-interacting excitons and their dynamics, towards macroscopic quantum states of matter such as Bose-Einstein condensates of excitons and polaritons. Momentum-direct layer-hybridized excitons in transition metal dichalcogenides have attracted considerable attention due to their high oscillator strength and dipolar nature. However, the tunability of their interactions and dynamics remains unexplored. Here, we achieve an unprecedented control over the nonlinear properties of dipolar layer-hybridized excitons in an electrically gated van der Waals homobilayer monitored by transient optical spectroscopy. By applying a vertical electric field, we reveal strong Coulomb interactions of dipolar hybrid excitons, leading to opposite density-dependent energy shifts of the two main hybrid species based on their dipolar orientation, together with a strongly enhanced optical saturation of their absorption. Furthermore, by electrically tuning the interlayer tunneling between the hybridized carriers, we significantly extend the formation time of hybrid excitons, while simultaneously increasing their decay times. Our findings have implications for the search on quantum blockade and condensation of excitons and dipolaritons in two-dimensional materials.

Extended efforts have been devoted to the study of strongly-interacting excitons and their dynamics, towards macroscopic quantum states of matter such as Bose-Einstein condensates of excitons and polaritons. Momentum-direct layer-hybridized excitons in transition metal dichalcogenides have attracted considerable attention due to their high oscillator strength and dipolar nature. However, the tunability of their interactions and dynamics remains unexplored. Here, we achieve an unprecedented control over the nonlinear properties of dipolar layer-hybridized excitons in an electrically gated van der Waals homobilayer monitored by transient optical spectroscopy. By applying a vertical electric field, we reveal strong Coulomb interactions of dipolar hybrid excitons, leading to opposite density-dependent energy shifts of the two main hybrid species based on their dipolar orientation, together with a strongly enhanced optical saturation of their absorption. Furthermore, by electrically tuning the interlayer tunneling between the hybridized carriers, we significantly extend the formation time of hybrid excitons, while simultaneously increasing their decay times. Our findings have implications for the search on quantum blockade and condensation of excitons and dipolaritons in two-dimensional materials.

Optical microcavities provide a powerful and versatile framework for manipulating the dynamics of photonic emission from optically active materials through light recirculation. Spatially indirect interlayer excitons (IXs) exhibit broad tunability of their emission energy via the quantum-confined Stark effect. However, the electrical tunability of IXs has not been exploited in cavity-coupled systems until now. Here we modulate the detuning between the cavity resonance and the IX emission in a monolithic Fabry–Perot cavity using an applied vertical electric field. We reveal a simultaneous enhancement of both the emission intensity and lifetime of weakly coupled IXs when in resonance with the optical cavity owing to strong Purcell inhibition and cavity transparency effects. We further investigate the tunable momentum dispersion of coupled IXs through back-focal-plane imaging and explain our results by the cavity coupling of IX transition dipoles as supported by theoretical modelling. Our work demonstrates an integration effort enabling the versatile tuning of highly interacting IXs within monolithic cavities, revealing the attractiveness of electrically tunable IX cavity coupling for both fundamental studies towards exciton condensate manipulation and future integration of excitonic devices.

Monolayers of transition-metal dichalcogenides, such as MoS₂, have attracted significant attention for their exceptional electronic and optical properties, positioning them as ideal candidates for advanced optoelectronic applications. Despite their strong excitonic effects, the atomic-scale thickness of these materials limits their light absorption efficiency, necessitating innovative strategies to enhance light-matter interactions. Plasmonic nanostructures offer a promising solution to overcome those challenges by amplifying the electromagnetic field and also introducing other mechanisms, such as hot electron injection. In this study, we investigate the vibrational and optical properties of MoS₂ monolayer deposited on gold substrates and gratings, emphasizing the role of strain and plasmonic effects using conventional spectroscopic techniques. Our results reveal significant biaxial strain in the supported regions and a uniaxial strain gradient in the suspended ones, showing a strain-induced exciton and carrier funneling effect toward the center of the nanogaps. Moreover, we observed an additional polarization-dependent doping mechanism in the suspended regions. This effect was attributed to localized surface plasmons generated within the slits, as confirmed by numerical simulations, which may decay nonradiatively into hot electrons and be injected into the monolayer. Photoluminescence measurements further demonstrated a polarization-dependent trion-to-A exciton intensity ratio, supporting the hypothesis of additional plasmon-induced doping. These findings provide a comprehensive understanding of the strain-mediated funneling effects and plasmonic interactions in hybrid MoS₂/Au nanostructures, offering valuable insights for developing high-efficiency photonic devices and quantum technologies, including polarization-sensitive detectors and excitonic circuits.